neutrons

[CPL.Luke]

what role does the neutron play in the atom? is it bound to the protons by the strong force?

[Jake712]

i believe its for stability reasons but i don't know any details.

[Gilded]

Stability indeed. They're bound together by strong nuclear forces.

 

Talking of neutrons, does anyone know how's the tetraneutron research? I haven't heard more than "it's possible that this sort of clusters exist".

[CPL.Luke]

what makes the atom more stable with a neutron than without one?

[swansont]

what makes the atom more stable with a neutron than without one?

 

Protons repel due to the electrostatic force. Neutrons only attract.

[CPL.Luke]

if quarks attract because of the strong force and neutrons and protons attract because of the strong force, then can you call an atomic nuclei a big ball of quarks?

[granDODyssey]

http://www.physlink.com/Education/AskExperts/ae565.cfm

 

excerpt from article from above link...

"the strong force only operates at EXTREMELY small distances. These distances are on the order of a 1000th millionth millionth of a meter (10 to the power of -15). If you think about a micrometer (one hundredth the size of a human hair), it is a billion times smaller than that.

 

The strong force also attracts protons to protons or neutrons to neutrons. In the case of protons to protons, the strong force loses strength after the distance mentioned above and succumbs to the electromagnetic force which pushes the protons apart."

 

All the atoms except the simplest , lightest ordinary hydrogen (atomic #1) have neutron(s), but what are they doing inside the atom? are they even neccessary? I'd like to think the following.....

 

When atoms get heavier(their atomic # increases), they have to be "bigger" also right?...which implies that the size of their nuclei grow larger too. The "strong force" which operates on 10^-15m distances is getting busier as nucleus size larger. If you think of a big nucleus with only protons, the "strong force" will get a hard time keeping together them in places, because protons do not like each other in terms of electrostatis(they both carry positive charges and "push" each other with electromagnetic force). this nucleus would be unlikely to be stable. ( rem...the strong force is only 137 times stronger than electromagnetic...)

 

but if you have some eletro-neural like neutrons around in the nucleus they should calms the "pushing" a little bit because they carry no charge and they don't repel each other...only glue each other and protons...so enforcing the "law and order" of sub-atomic realm?????...

[CPL.Luke]

but still the question remains why do neutrons repel protons to a certain extent so that you are incapable of calling an atomic nucleus a ball of quarks

 

is this the role of the weak force?

[granDODyssey]

neutrons do not repel protons or each other....when they are in a atomic nucleus...they all are glued together by strong force..when they are free in outside world, that's another story of course.(...)

only protons repel each other with electromagnetic for only 137 times weaker than the strong force which holds them together.

 

"The composition of the proton is a combination of 3 quarks -- 2 up and 1 down quarks. For the neutron, the combination is 1 up and 2 down quarks. "

 

of course, the strong force is also the one responsible for holding these quarks together...but still you can consider a proton ...proton ...(not 3 quarks) i guess

 

the weak force is known to be responsible for nuclear reaction involving atomic decay in some elements like radium ..etc

[Severian]

You have to remember why the three quarks bind together in the first place. In electromagnetism (QED) the particles have an electric charge (which may be zero): they like to bind together into objects which are neutral. The 'color force' (QCD) has three colors, so it is not quite as simple as QED. An object is colour neutral if it has all three colors equally balanced.

 

So a proton is a uud composite where each quark has a different color, and a neutron is likewise a udd composite with no net color. (The 3 colors of QCD is why baryons have 3 quarks.)

 

Now, if they were bound together at a point, they would be color neutral and there would be no further effects from QCD. It would not contribute to binding nuclei together.

 

But they are not bound at a point, so if you are standing(!) close enough to the proton, the color force from the closer quark will not be perfectly balanced by the others (since they are further away) and therefore you will feel a net color force. But since this is a 'residual' force, it will be much weaker than the raw QCD. This is what binds nuclei together.

 

Since the neuton is, in terms of residual QCD, almost identical to the proton, it plays just as important a roll in holding together the nuclei. In fact, as someone pointed out, it is easier to bind together since you don't have to overcome the repulsion of too like charge protons....

[swansont]

All the atoms except the simplest ' date=' lightest ordinary hydrogen (atomic #1) have neutron(s), but what are they doing inside the atom? are they even neccessary? I'd like to think the following.....

 

When atoms get heavier(their atomic # increases), they have to be "bigger" also right?...which implies that the size of their nuclei grow larger too. The "strong force" which operates on 10^-15m distances is getting busier as nucleus size larger. If you think of a big nucleus with only protons, the "strong force" will get a hard time keeping together them in places, because protons do not like each other in terms of electrostatis(they both carry positive charges and "push" each other with electromagnetic force). this nucleus would be unlikely to be stable. ( rem...the strong force is only 137 times stronger than electromagnetic...)

 

but if you have some eletro-neural like neutrons around in the nucleus they should calms the "pushing" a little bit because they carry no charge and they don't repel each other...only glue each other and protons...so enforcing the "law and order" of sub-atomic realm?????...[/quote']

 

That's basically it. But the electrostatic force is infinite in range, and the strong force isn't, so the strong force "saturates" and you need more and more neutrons as the nucleus gets larger. Eventually you reach a point where even that fails to provide stability, and you get alpha decay or spontaneous fission for the very large nuclei. (There are also effects because of the shell structure that explain beta decays)

 

From an energy standpoint, nuclei with about 60 nucleons are the most tightly bound. Fusion of light nuclei and fission of heavy nuclei release energy, with ~60 being the line of demarcation. Generally you can't fission light nuclei or fuse heavy ones unless you add energy.

[CPL.Luke]

one last question

 

what is the weak forces role in the atom it sounds like it would be so completely counterballanced by the strong force that it shouldn't even be considered in atomic nuclei

 

I know that this isn't the case as some work is spent on it so can anyone explain it a bit more

[Severian]

The weak force has no role in binding the nucleus together, but it does cause radioactive decay of the nuetron. This is discussed in another thread: http://www.scienceforums.net/forums/showthread.php?t=6972